Establishes a buffer for selection mode values.
OpenGL C bindings library: libGL.a
void glSelectBuffer(GLsizei Size, GLuint *Buffer)
| Size | Specifies the size of Buffer. |
| Buffer | Returns the selection data. |
The glSelectBuffer subroutine has two arguments: the Buffer parameter is a pointer to an array of unsigned integers, and the Size parameter indicates the size of the array. Buffer returns values from the name stack when the rendering mode is GL_SELECT. (See the glInitNames subroutine for information on initializing the name stack; the glLoadName subroutine for information on loading names onto the name stack; the glPushName subroutine for pushing and popping the name stack; and the glRenderMode subroutine for information on setting the rasterization mode.) The glSelectBuffer subroutine must be issued before selection mode is enabled, and it must not be issued while the rendering mode is GL_SELECT.
Selection is used by a programmer to determine which primitives are drawn into some region of a window. The region is defined by the current modelview and perspective matrices.
In selection mode, no pixel fragments are produced from rasterization. Instead, if a primitive intersects the clipping volume defined by the viewing frustum and the user-defined clipping planes, this primitive causes a selection hit. (With polygons, no hit occurs if the polygon is culled.) When a change is made to the name stack, or when the glRenderMode subroutine is called, a hit record is copied to Buffer if any hits have occurred since the last such event (name stack change or glRenderMode call). The hit record consists of the number of names in the name stack at the time of the event, followed by the minimum and maximum depth values of all vertices that hit since the previous event, followed by the name stack contents, bottom name first.
Returned depth values are mapped such that the largest unsigned integer value corresponds to window coordinate depth 1.0, and 0 (zero) corresponds to window coordinate depth 0.0.
An internal index into Buffer is reset to 0 whenever selection mode is entered. Each time a hit record is copied into Buffer, the index is incremented to point to the cell just past the end of the block of names, that is, to the next available cell. If the hit record is larger than the number of remaining locations in Buffer, as much data as can fit is copied, and the overflow flag is set. If the name stack is empty when a hit record is copied, that record consists of 0 followed by the minimum and maximum depth values.
Selection mode is exited by calling glRenderMode with an argument other than GL_SELECT. Whenever glRenderMode is called while the render mode is GL_SELECT, it returns the number of hit records copied to Buffer, resets the overflow flag and the selection buffer pointer, and initializes the name stack to be empty. If the overflow bit was set when glRenderMode was called, a negative hit record count is returned.
The contents of Buffer are undefined until glRenderMode is called with an argument other than GL_SELECT.
The glBegin/glEnd subroutine primitives and calls to glRasterPos can result in hits.
Associated gets for the glSelectBuffer subroutine are as follows. (See the glGet subroutine for more information.)
glGet with argument GL_NAME_STACK_DEPTH.
glGetPointerv with argument GL_SELECTION_BUFFER_POINTER.
| /usr/include/GL/gl.h | Contains C language constants, variable type definitions, and ANSI function prototypes for OpenGL. |
The glBegin or glEnd subroutine, glFeedbackBuffer subroutine, glGetPointerv subroutine, glInitNames subroutine, glLoadName subroutine, glPushName subroutine, glRenderMode subroutine.